The instant invention pertains to methods and apparatus for raising and lowering a telescoping mast and more particularly to such methods and apparatus which may be employed in a limited space, e.g., on an offshore platform.
In the drilling of an oil and gas well, a portable mast is usually used to support the drill string during drilling. After the well is completed, the mast is moved to a different location for drilling another well. To facilitate such portability, the mast is constructed to be divided into sub-assemblies during transporation. One such mast is of the telescoping variety which typically comprises an elongate lower section adapted to be mounted on a base surrounding a proposed wellbore and an elongate upper section which is slidably received, for example by a pulley system, within the lower section.
Many telescoping masts are constructed to be extended and contracted in a vertical position. That is, when the mast arrives at a location at which a well is to be drilled, the lower section, having the upper section received therein, is mounted on a base surrounding the proposed wellbore. Thereafter, rigging or hydraulic power is used to slide the upper section upwardly out of the lower section to its uppermost extended condition. When such condition is assumed, the upper section is mechanically spliced to the lower section to increase the rigidity of the mast.
Telescoping masts designed for erection in the vertical position as described above suffer from several disadvantages. One disadvantage is that in its extended condition, the axes of the elongate beams in the upper and lower mast sections are offset relative to one another which produces a less stable mast than if the beams are in coaxial alignment. U.S. Pat. No. 2,804,948 to Woolslayer et al. discloses a telescopting portable mast which includes an upper section that is slidably received substantially within a lower section. In its extended condition, the elongate beams in the upper and lower sections, which form the primary support for the mast in its vertical position, are in coaxial alignment with one another. The Woolslayer et al. '948 patent teaches extension of the mast in a horizontal position since the elongate support beams in the upper section must move laterally with respect to the elongate support beams in the lower section to produce coaxial alignment in the extended condition. Extension of the mast in a horizontal position is not possible when space is limited, for example on an offshore drilling platform.
It is a general object of the present invention to provide a method and apparatus for raising and lowering a telescoping mast.
It is a more specific object of the invention to provide such a method and apparatus in which the mast is not extended or contracted in a vertical or horizontal position.
It is another specific object of the invention to provide such a method and apparatus which requires less space than that required to extend the mast in a horizontal position.
It is yet another specific object of the invention to provide such a method and apparatus which pivots the mast to a vertical position during mast extension and pivots the mast to a horizontal position during mast contraction.
It is still another object of the invention to provide such a method and apparatus which utilizes the same power source to pivot and extend the mast.